The seaducks, Merginae, form a subfamily of the duck, goose and swan family of birds, Anatidae.
As the name implies, most but not all, are essentially marine outside the breeding season. Some of the mergansers prefer riverine habitats.
All but two of the 20 species in this group occupy habitats in far northern latitudes.
The fish-eating members of this group, such as the mergansers and Smew, have serrated edges to their bills to help them grip their prey. These are therefore often known as "sawbills".
Other seaducks take molluscs or crustaceans from the sea floor
There are twenty species in ten genera.
Subfamily Merginae
- Genus Polysticta
- Genus Somateria, the eiders. These are large marine ducks The drakes have body plumage showing varying amounts of black and white, and distinctive head patterns.Females are brown.
- Genus Histrionicus
- Genus Camptorhynchus
- Genus Melanitta, the scoters. These are stocky marine ducks. The drakes are mostly black and have swollen bills. Females are brown.
- Genus Clangula
- Genus Bucephala, the goldeneyes. These are less marine than some species in this group, and will winter on fresh water. Drakes have white bodies with black backs and distinctive head markings. Females are grey with chestnut heads.
- Genus Mergellus
- Genus Lophodytes
- Genus Mergus, the typical mergansers. These are the least marine of this group, only Red-breasted being common on the sea. These are large saw-billed ducks which dive for fish.
- Brazilian Merganser Mergus octosetaceus
- Auckland Island's Merganser Mergus australis (extinct)
- Red-breasted Merganser Mergus serrator
- Common Merganser or Goosander Mergus merganser
- Chinese Merganser Mergus squamatus
